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Hey everyone! This is my first post on this forum. Hoping you guys might be able to give me some pointers on why I might be experiencing the issues that I am having with my MK I build. This pedal has been kicking my butt and while Iím fairly confident that I just havenít been able to get the proper transistor combo sorted out yet, I wanted to seek some clarification as it relates to this circuit. Iíve searched and searched for information on things like transistor voltages, target gain and leakage, etc. While there are quite a few threads out there that already broach these topics, it seems there is no ďone size fits allĒ answer. Quite different than something like the fuzz face circuit. Iíve built the Gary Hurst version of the pedal, and while the pedal does work, I cannot seem to dial out the overly sizzly decay. Itís become quite the time consuming and frustrating process of measuring and selecting transistors, plugging them in, only to still have essentially the same result each time I play through the pedal. I understand the MKI is primitive and sizzle/gating are commonly associated with this circuit, but mine seems overly obnoxious and unpleasant. Iíve owned MKI builds that didnít do this. The fuzz tone is not bad on mine at all, but the way notes fade out really drives me a bit nuts. It has quite a gate to it as well. Things Iíd like to seek information on are the following:

What are target voltages on each legs of the transistors that I should shoot for?

Should Q1 base and Q1 emitter voltage essentially be equal? Every time I put transistors in my circuit to test, I do a voltage check first and have taken notes on different combos and values. I am noticing the voltage on Q1 base and emitter are basically equal. Is this normal or indicative of a problem?

What should I be aiming for in terms of leakage and gain on my transistors? I see what small bear shoots for in their MKI transistor combo, but have read forums where people have shared positive results with some values that differ quite substantially from one another. Everyone has their own ear but whatís more crucial here? Gain or leakage or both?

Iíve noticed if the transistors are too leaky, the pedal will squeal and make noise even if Iím not playing or touching the guitar. It seems like the window of satisfactory leakage and gain(more leakage though) is VERY small.

Whatís the potential main influencer of sizzle on the note decay? Itís excessive in my build. I can see maybe a little but itís quite intense with mine. No combo Iíve put in the pedals has really made a huge impact up to this point. Iíve measured Q2 collector voltages anywhere from 2v up to 8v, with sizzle being present in all scenarios.

Are there some transistors that just donít work in this circuit? Some people definitely seem to believe so. I have picked through my whole stash which consists currently of:

2N404 and 2N414 (STI)

So far the best combo I had noted down so far was:

Q1 = MP16B. Roughly 66 hfe, 104 mA leakage
Q2 = SFT353. Roughly 70 hfe, 590 mA leakage
Q3 = 2N404. Roughly 100 hfe, 62 mA leakage

Voltages with this combo:

Q1 collector: 9.18
Q1 base: 0.517
Q2 emitter: 0.47

Q2 collector: 5.81
Q2 base: 0.131
Q2 emitter: 0

Q3 collector: 9.09
Q3 base: roughly 8-10 mV
Q3 emitter: 0

Iíve seen people suggest q3 needs low to no leakage. Iíve seen other say this for q2 instead. Iíve seen others say that all positions needed higher leakage to work for them. The uncertainty with how to approach this circuit is something that I guess keeps a lot of builders away. Iíd really like to get this thing dialed in and so Iím hopeful someone here can guide me!

Iíve tried higher leakage trannies in Q1 and Q2. Iíve tried high leakage in q1 and low leakage in q2. Iíve tried higher leakage in all positions. Iíve tried as many combos as my stash has allowed and am essentially not making much progress. I am considering investing in some more transistors, but wanted to put this thread out to the world first.

I appreciate any tips or suggestions anyone has! Thanks for reading!!

Building your own stompbox / Re: A 4046 based synth demonstrator
« Last post by strungout on Yesterday at 09:38:55 PM »
This thread was necro'ed!

But, @ Ben N: All of them have their own flavors but I think I liked the pulse and saw most. Just now, I was playing with mixing 2 waves together. A lot of wobble happens (Square + mix for example). It'S interesting. But there's some volume issues... Think I might start another thread to figure out that stuff.
Building your own stompbox / Re: Logic chip, flip flop, or relay?
« Last post by Matthew Sanford on Yesterday at 09:35:15 PM »
HmmmÖwondering if I figure the voltage drop from in to out on the 157, if I can feed one from the pots, adjust it after, then would it hold the voltage? OrÖmaybe look for a Schmitt trigger one, then it should hold and I can switch the after parts. Something I need to learn on, but thatís what holds its output state steady, regardless of input changes, yea?

Ok, thank you on this, Iíll riddle through a bit moreÖ
Building your own stompbox / Re: Wider enclosures, Sansamp fly rig style
« Last post by bluelagoon on Yesterday at 08:50:05 PM »
Save yourself some time money, and spare yourself the headaches, just get on over to Aliexpress and purchase a cheap as chips already assembled no components needed, no assembly required multi fx pedal similar to the Sans amps for not much more than your Porsche rocker cover worst nightmare.

Building your own stompbox / Re: Aion Theseus (KoT) issues
« Last post by RickMcCarthy on Yesterday at 08:21:14 PM »
I would triple-check and make sure the Vbias resistors (R12 and R13) are correct... if R12 was 47R instead of 47k then it would cause voltages pretty much exactly as measured. There are a few other 47R resistors in the circuit, so it would be an easy mistake to make since all but one of the color bands are the same.

I did have the correct value on R12 & 13. What about no voltage in C10? There is a trace from the intersection of R12&13 to the + pad on C10, correct? The working ďBĒ side has voltage on + pad of C20 and thatís one of the more telling differences I can find. I even changed C10 to another cap but nothing. Am I after a red herring?
Building your own stompbox / Re: Aion Theseus (KoT) issues
« Last post by RickMcCarthy on Yesterday at 08:17:56 PM »
Not a fried chip. Being a dual pedal I was able to swap the chips and both work in side ďBĒ so I think that rules out a bad op amp.
Building your own stompbox / Re: Add tone stack to a Buss Fuzz
« Last post by Dormammu on Yesterday at 07:38:57 PM »
Continuity is ok, but no sound no matter the cap size
Does the circuit itself work ?
Building your own stompbox / Re: pedal building education
« Last post by PRR on Yesterday at 07:37:32 PM »
{quote lost?}> I cannt find this book except in Kindle form...

You do not need a hunret-buck Kindle to read kindles. There is a web-interface (, App for Android (prolly iPhone), application for Windows (recent versions; but a Win7 install lurks in the wild), maybe Mac too?

When you shop for the e-book, also look for this link:

Building your own stompbox / Re: Logic chip, flip flop, or relay?
« Last post by ElectricDruid on Yesterday at 06:00:19 PM »
any tricks to have it remember settings? Iím guessing digital pots or something.

Well, the chips are expecting a 0-5V CV, so anything that produces that is fine. That means a DAC, digital pots, an Arduino's PWM outputs (with a bit of filtering), whatever. It's all shouting "PROCESSORS!" at me at that point though - remembering settings is a job for microprocessors and code, in whatever form you like best.
Building your own stompbox / Re: Add tone stack to a Buss Fuzz
« Last post by antonis on Yesterday at 05:01:10 PM »
It's time for audio probe then.. :icon_wink:

edit: Before audio probing, I'd check for shorted tonestack caps..
(especially for 47nF one..)
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